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How do I share a global variable with thread?
My Python code example is:
from threading import Thread import time a = 0 #global variable def thread1(threadname): #read variable "a" modify by thread 2 def thread2(threadname): while 1: a += 1 time.sleep(1) thread1 = Thread( target=thread1, args=("Thread-1", ) ) thread2 = Thread( target=thread2, args=("Thread-2", ) ) thread1.join() thread2.join() I don't know how to get the two threads to share one variable.
629
But to answer your question, any thread can access any global variable currently in scope. There is no notion of passing variables to a thread. It has a single global variable with a getter and setter function, any thread can call either the getter or setter at any time.
Almost certainly. I answered the question in a very narrow sense: how do I modify a global variable, without any consideration for how you modify it safely.
We can protect the global variable from race conditions by using a mutual exclusion lock via the threading. Lock class. First, we can create a lock at the same global scope as the global variable. Each time the global variable is read or modified, it must be done so via the lock.
You just need to declare a as a global in thread2, so that you aren't modifying an a that is local to that function.
def thread2(threadname): global a while True: a += 1 time.sleep(1) In thread1, you don't need to do anything special, as long as you don't try to modify the value of a (which would create a local variable that shadows the global one; use global a if you need to)>
def thread1(threadname): #global a # Optional if you treat a as read-only while a < 10: print a If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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